1. Field of the Invention
This invention relates to a method and apparatus for determining volume, form and weight of an object, and more particularly, such a method and apparatus using a camera.
2. Description of the Related Art
In the processing of fish and other products it is necessary to grade and sort portions into various categories, both by form (i.e. whether they are tail portions, loins, center portions, etc.) and by weight. It is also sometimes convenient to grade fish fillets before they are portioned. At present, grading by form is carried out by hand, and then each portion is weighed. This method is time consuming and is subject to error. Grading by weight alone is of little value, because it does not provide information on the flesh distribution of the fish sufficient for further processing. By analyzing the form and the volume in addition to the weight of the product, significantly more information can be obtained and used in determining the further processing of the fish.
One technique which has frequently been applied to measure the three-dimensional form of objects is "structured lighting", in which a pattern of lines is projected onto the object at a particular angle and then examined from another angle with a camera. The application for patent of ISHIDA European Patent Application No. 85306694.2 provides one example of this technique. The principal disadvantage of the structured lighting measuring technique is that there must be a specific minimum distance between the lines which are projected onto the fish so that they do not overlap. A common interval is 21/2 cm, i.e. 0.4 lines per cm, and it is seldom that more than 50 points along each line are measured, so that only 20 measuring points are obtained for each cm along an object. If the quantization error in structured lighting is examined, it is evident that the error is extremely large. For example, 50 cm is imaged with 256.times.256 pixels and there is an interval of 21/2 cm between the lines which are projected onto the fish. Approximately 20 lines are therefore projected onto a fish, and the thickness along each line is measured by 13 pixels. Frequently, the thickness is measured with 5-10 pixels. It is therefore clear that there will be considerable error due to the low resolution of the method. Another substantial disadvantage of structured lighting is that a large amount of data must be processed: 256.times.256, or 65,536 measuring points, and extremely complex image analysis techniques are needed in order to determine the size and position of the fish on the basis of such data. This calculation intensive method results in a slow operation and limited accuracy.